Solid propellant rocket

ABSTRACT

A method and apparatus for utilizing the volatility of the combustion products of solid metallic propellants to accelerate metal combustion products to gaseous velocity by recondensing the gaseous products in the rocket envelope behind the throat of the nozzle. A further useful effect is accomplished by the reaction between the steam formed in the condensation reaction and an added fuel to form additional moles of working gas.

United States Patent Camp et a].

[451 June 13,1972

1 1 SOLID PROPELLANT ROCKET [72] Inventors: Albert T. Camp, Indian Head;Alan Mc- Cone, Jr., Hyattsville, both of Md.

221 Filed: Jan. 30, 1967 21 Appl.No.: 614,525

[52} US. Cl. .60/207, 60/219, 60/220,

60/251, 60/253, 239/127.3, 239/265.15 [51) Int. Cl. ,.C06d 5/00, F23r1/00 [58] Field of Search ..60/204, 207, 220, 231, 253',

[ 56] References Cited UNITED STATES PATENTS Skinner ..60/253 Fox.60/207 3,133,413 5/1964 Lawrence ..60/224 3,158,061 11/1964 Lager 1..60/250 3,176,618 4/1965 Forsberg et a1.. .....60/2S3 3,292,376 12/1966Ernst et al..,. 239/265.17 3,304,722 2/1967 Cuipepper ..60/271 PrimaryE.taminerSamuel Feinberg Attorney-R. S. Sciascia and .11 A. Cooke 57ABSTRACT A method and apparatus for utilizing the volatility of thecombustion products of solid metallic propellants to accelerate metalcombustion products to gaseous velocity by recondensing the gaseousproducts in the rocket envelope behind the throat of the nozzle. Afurther useful effect is accom plished by the reaction between the steamformed in the condensation reaction and an added fuel to form additionalmoles of working gas.

15 Claims, 1 Drawing Figure PATENTEDJUH 13 m2 INVENTORS Albert T CampAlan McCon e, Jr

NEY

AGENT BACKGROUND OF THE INVENTION The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

This invention relates to solid propellant rockets and more particularlya method and apparatus for using fuels containing a light metal such asberyllium, boron, aluminum, magnesium, zirconium, titanium, lithium,silicon, aluminum borohydride and the hydrides of the metals in solidpropellant rocket motors.

Heretofore, fuels such as beryllium, boron, aluminum, magnesium,zirconium, titanium, lithium, silicon, aluminum borohydride and thehydrides of the metals have not found effective practical application insolid propellant rockets due mainly to inefficiencies in combustion.Theoretically, these metals and hydrides offer very substantial gains inspecific impulse of propellants. All the metals form hydroxides whichare volatile at temperatures encountered in rocket propellantcombustion. But advantage of this volatility has not been taken toaccelerate the metal combustion products to gaseous velocity prior totheir condensation within the rocket nozzle expansion cone to therebyimprove specific impulse.

All accepted thermochemical data to the contrary, recent rocketevaluations of certain beryllium modified solid propellants have shownthat gaseous species of oxidized beryllium are formed in significantproportions during the combustion or expansion process. The most likelygaseous species are H O Be-O-H, HOBeCl, BeCl and BeOH. The importantmembers of these species form and persist at rather high temperatures,as they are less easily dissociated than steam, and remain gaseous untilcooled to about l,200 C. Such a low temperature is not ordinarilyreached in a rocket nozzle expansion cone; thus, except at extremelyhigh expansion ratios, one or more gaseous beryllium compounds wouldnormally leave the expansion cone as a gas containing substantial latentheat of vaporization. This phenomenom helps explain the consistent lossof specific impulse efficiency encountered with beryllium propellants atintermediate expansion ratios of 25 to l to 50 to I.

SUMMARY OF THE INVENTION It is an object of this invention to provide asolid propellant rocket apparatus and method of using fuels containing alight metal such as beryllium, boron and aluminum magnesium, zirconium,titanium, lithium, silicon, aluminum borohydride and the hydrides of themetals, wherein the gaseous species of the oxidized metal formed duringthe combusion or expansion process is cooled sufficiently to extract thelatent heat of vaporization and thus increase the specific impulseefficiency.

The above and other objects are generally accomplished in a solidpropellant rocket motor by cooling the products of combustion of themetal downstream of the throat of the expansion nozzle by injecting apressurized gaseous fuel. The gaseous fuel injected into the rocketnozzle mixes efticiently with the rocket combustion products to provideadditional moles of gas for thrust augmentation and any desired thrustvector control effect as needed. Additionally the gaseous products ofcombustion are first cooled before reaching the throat of the expansionnozzle by passing through a ring of ablative material to thus initiatecooling to insure that the cooling process in the expansion nozzle issufiicient to remove the latent heat of vaporization of the gaseouscombustion products.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of thisinvention and many of its attendant advantages will be readily apparentas the same becomes better understood by reference to the followingdetailed description when considered in conjuction with the accompanyingdrawing wherein the single FIGURE is a sectional view of the rocketmotor of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, thereis shown generally a rocket motor casing 10 enclosing a pressure chamberI2 having a highly oxidized solid propellant 14 containing a powderedlight fuel such as beryllium, boron, aluminum, magnesium, zirconium,titanium, lithium, silicon, aluminum borohydride and the hydrides ofthese metals therein. The solid propellant can contain as majorconstituents a suitable polymeric binder selected from the groupconsisting of plasticized double-based nitrocellulose, polybutadiene,polyurethane, polysulfidehydrocarbon, polyisobutylene andpolyvinylchloride and at least one oxidizer from the group consisting ofammonium perchlorate, potassium perchlorate hydroxylammon iumperchlorate, nitronium perchlorate, h ydrazinium diperchlorate,hydrazinium nitroform ate,

cyclotetramethylene tetranitramine and cyclotrimethylene trinitramine.

The rocket casing 10 at its rear portion 16 forms a suitable indentednozzle throat portion 18 that is sealed initially by a suitable igniterand frangible nozzle plug 20. The casing 10 immediately after the throatportion 18 flares radially outward to form a conventional nozzleexpansion envelope or cone 22 wherein the gaseous products of combustionmay expand and accelerate.

A toroidal tank 24 is arranged externally of the nozzle throat area 18having connecting passages 26 communicating with the expansion envelope22 of the rocket through inlet ports 28 arranged circumferentially inthe wall of the expansion envelope. The pressurized tank 24 contains afuel selected from the group consisting of the alkanes such as methane,ethane, propane, butane, heptane and dodecane, the alkenes such asethylene and propylene, an alkyne such as acetylene, methyl acetylene,ammonia, aniline, ethylamine, methylarnine, ethylene diamine,o-toluidine, triethyl amine, hydrazine, unsymmetrical dimethylhydrazine, monomethylhydrazine, dimethylenetriamine, furfuryl alcohol,ethyl alcohol, butylene, butadiene, or mixtures thereof and suspensionsof carbon in any of the above. The fuel from tank 24 is injected intothe expansion nozzle 22 so as to mix effectively with the rocketcombustion products thereby reacting with them and cooling them toprovide additional moles of gas for thrust augmentation and any desiredthrust vector control effect as needed.

A cast ring 30 composed of a fuel rich material comprising 30-50 percentsynthetic rubber compound rich in hydrocarbons selected from the groupconsisting of polybutadiene, polyurethane, polysulfide-hydrocarbon,polyisobutylene, polyvinylchloride, polyethylene, polypropylene andpolyisoprene, 1030 percent carbon black and 15-40 percent ofanitroamine, such as l, 3, 5, 7 tetranitro l, 3, 5, 7 tetraza cycloctane(HMX) or I, 3, 5 trinitro l, 3, 5 triazacyclohexane (RDX) is internallysituated just in front of the throat 18 of the nozzle. The hot gases ofthe combustion products pass through the cast ring 30 and are partiallycooled but not condensed before they reach the throat 18 of the nozzle.The cast ring ablates away to take away heat and reacts with the hotgases of combustion.

To illustrate the general operation of the rocket system, a solidpropellant having powdered beryllium will be described with theunderstanding that any of the other light metals and hydrides would worksimilarly. Initially, the igniter 20 is actuated to begin the combustionprocess of the solid propellant fuel containing the powdered beryllium.The highly oxidized propellant has a combustion temperature of about3,000 to 4,000 C. Among the products of combustion of the solidpropellant are beryllium dihydroxide and possibly BeOH and BeOHCl ingaseous form and in molten globular form and H 0 gas. At combustiontemperatures the BeO and steam react to form gaseous Be(OH) This gaseousberyllium dihydroxide is less easily dissociated than steam and persistsat rather high temperatures and remains gaseous until about 1,200" C.Such a low temperature is not ordinarily reached within a nozzleexpansion cone and thus except at extremely high expansion gaseousberyllium dihydroxide can be cooled to a range of 900 to 1,500 C thereaction proceeds to form solid BeO crystals in a particle size of 0.01to 0.5 micron size and steam. By this added reactive step the mostefficient utilization of the combustion of the powdered beryllium isaccomplished as the latent heat of vaporization is recovered in theexpansion nozzle. Impulse efficiencies of 98 percent are therebyobtainable in contrast with only 93 percent efficiencies obtained whenthe metal oxides remain always in the condensed state throughoutcombustion.

To achieve the necessary cooling to obtain the desired recondensationwithin the rocket envelope and the resultant finely divided condensedspecies it is necessary to cool the combustion gases as the necessaryhigh expansion ratios are practically unachievable within sizelimitations that are essential. A first stage of cooling prior to thecombustion gases reaching the throat area of the nozzle is obtained byallowing the hot gases to pass through the cast ring 30 which thenablates away and by endothermic reaction causes a partial cooling butnot condensation. Further cooling may be efiected in the expansion coneby the injection of the pressurized fuel from toroidal tank 24 to bringthe exhaust temperature down to l,200 C thereby to effectuate completecondensation. Additionally, the injected fuel reacts with the steam toprovide additional moles of working gas, for example if methane is usedthe reaction would be H O CH. 3H CO, and thus two moles of reactantwould provide 4 moles of working gas.

Thus it can be seen that by allowing the metallicoxide gas to condensesufficiently to give up its latent heat of vaporization and to formsubmicron size crystal particles to allow complete utilization of allheat, impulse etficiency can be maximized.

Obviously numerous modifications and variations of the invention arepossible in the light of the above teachings. it is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described herein.

We claim:

1. In a solid rocket propulsion motor, a rocket casing comprising,

a pressure chamber containing an oxidizer, polymeric binder, and apowdered light fuel,

means for initiating combustion of the contents of said chamber,

said pressure chamber terminating at one end in an indented nozzlethroat,

said nozzle throat flaring radially outward to form a nozzle expansioncone,

means communicating with said nozzle expansion cone to cool the gaseousproducts of combustion after said gaseous products of combustion havepassed said nozzle throat comprising a toroidal tank positioned exteriorto said rocket casing,

connecting passages from said toroidal tank to said nozzle expansioncone,

inlet ports in the walls of said nozzle expansion cone,

said connecting passages communicating with said inlet ports to providecommunication between said toroidal tank and said nozzle expansion cone,wherein said toroidal tank contains a pressurized fuel selected from thegroup consisting of alkanes, alkenes, and alkynes.

2. The rocket motor of claim 1 wherein the oxidizer is selected from thegroup consisting of ammonium perchlorate, potassium perchlorate,hydroxylammonium perchlorate, nitronium perchlorate, hydraziniumdiperchlorate, hydrazinium nitroformate, cyclotetramethylenetetranitramine and cyclotrimethylene trinitramine.

3. The rocket motor of claim 1 wherein the polymeric binder is selectedfrom the group consisting of plasticized double-based nitrocellulose,polybutadiene, polyurethane, polysulfide-hydrocarbon, polyisobutyleneand polyvinylchloride.

4. The rocket motor of claim 1 wherein the powdered light fuel isselected from the group consisting of beryllium, boron, aluminum,magnesium, zirconium, titanium, lithium, silicon, aluminum borohydrideand the hydrides of the metals.

5. The rocket system of claim 1 wherein the powdered light fuel isberyllium.

6. The rocket motor of claim 1 wherein the alkanes are selected from thegroup consisting of methane, ethane, butane, propane, heptane anddodecane, the alkenes are selected from the group consisting of ethyleneand propylene and the alkyne is acetylene.

7. The rocket motor of claim 6 wherein said pressurized fuel containsfine suspensions of carbon.

8. The rocket motor of claim 1 including means within said pressurechamber adjacent said throat for initially partially cooling the gaseousproducts of combustion prior to their passage through the throat.

9. The rocket motor of claim 8 wherein said means for initiallypartially cooling the gaseous products of combustion includes a castring comprising 30-50 percent synthetic rubber compound rich inhydrocarbons, l0-30 percent carbon black and lS-40 percent nitroaminethat reacts with the hot products of combustion and provides anendothermic reaction to remove heat.

l0. The rocket motor of claim 9 wherein the synthetic rubber compound isselected from the group consisting of polybutadiene, polyurethane,polysulfidehydrocarbon, polyisobutylene, polyvinylchloride,polyethylene, polypropylene and polyisoprene and the nitroamine isselected from the group consisting of l,3,5,7 tetranitrol ,3,5,7tetrazacycloctane and l,3,5 trinitrol ,3,5 triazacylcohexane.

11. A process for achieving high specific impulse in a solid propellantrocket motor, comprising combusting a solid propellant containing anoxidizer,

polymeric binder and a powdered light fuel selected from the groupconsisting of beryllium, boron, aluminum, magnesium, zirconium,titanium, lithium, silicon, aluminum borohydride and the hydrides of themetals, to form as part of the products of combustion a mixture of steamand the oxide of the light metal,

allowing said mixture to react at combustion temperatures to form themetal hydroxide gas, and

cooling said metal hydroxide gas to a temperature sufficient to releasethe latent heat of vaporization of said metal hydroxide gas and formmetal oxide crystals in a particle size of 0.0! to 0.5 microns andsteam, said cooling being accomplished by injecting a pressurized fuel,selected from the group consisting of alkanes, alkenes, and alkynes, andmixtures thereof, into the metal hydroxide gas while it is expanding.

12. The process of claim 11 wherein said combustion temperature is inthe range of 3,000 to 4,000 C and said cooled temperature is in therange of 900 to 1,500 C.

13. The process of claim 11 wherein the alkanes are selected from thegroup consisting of methane, ethane, butane, propane, heptane anddodecane, the alkenes are selected from the group consisting of ethyleneand propylene and the alkylene is acetylene.

14. The process of claim 11 wherein said cooling step is initiated byfirst passing said products of combustion through a cast ring comprising30-50 percent synthetic rubber compound rich in hydrocarbons, 10-30percent carbon black and 15-40 percent nitroamine to react with saidproducts of combustion endothermically to remove heat from said productsof combustion prior to expansion.

15. The process of claim 14 wherein the synthetic rubber compound isselected from the group consisting of polybutadiene, polyurethane,polysulfide-hydrocarbon, polyisobutylene, polyvinylchloride,polyethylene, polypropylene and polyisoprene and the nitroamine isselected from the group consisting of l,3,5.7 tetranitro-l ,3,5,7tetrazacycloctane and 1,3,5 trinitro-l ,3,5 triazacyclohexane.

II Il III i

2. The rocket motor of claim 1 wherein the oxidizer is selected from thegroup consisting of ammonium perchlorate, potassium perchlorate,hydroxylammonium perchlorate, nitronium perchlorate, hydraziniumdiperchlorate, hydrazinium nitroformate, cyclotetramethylenetetranitramine and cyclotrimethylene trinitramine.
 3. The rocket motorof claim 1 wherein the polymeric binder is selected from the groupconsisting of plasticized double-based nitrocellulose, polybutadiene,polyurethane, polysulfide-hydrocarbon, polyisobutylene andpolyvinyl-chloride.
 4. The rocket motor of claim 1 wherein the powderedlight fuel is selected from the group consisting of beryllium, boron,aluminum, magnesium, zirconium, titanium, lithium, silicon, aluminumborohydride and the hydrides of the metals.
 5. The rocket system ofclaim 1 wherein the powdered light fuel is beryllium.
 6. The rocketmotor of claim 1 wherein the alkanes are selected from the groupconsisting of methane, ethane, butane, propane, heptane and dodecane,the alkenes are selected from the group consisting of ethylene andpropylene and the alkyne is acetylene.
 7. The rocket motor of claim 6wherein said pressurized fuel contains fine suspensions of carbon. 8.The rocket motor of claim 1 including means within said pressure chamberadjacent said throat for initially partially cooling the gaseousproducts of combustion prior to their passage through the throat.
 9. Therocket motor of claim 8 wherein said means for initially partiallycooling the gaseous products of combustion includes a cast ringcomprising 30-50 percent synthetic rubber compound rich in hydrocarbons,10-30 percent carbon black and 15-40 percent nitroamine that reacts withthe hot products of combustion and provides an endothermic reaction toremove heat.
 10. The rocket motor of claim 9 wherein the syntheticrubber compound is selected from the group consisting of polybutadiene,polyurethane, polysulfide-hydrocarbon, polyisobutylene,polyvinylchloride, polyethylene, polypropylene and polyisoprene and thenitroamine is selected from the group consisting of 1,3, 5,7tetranitro-1,3,5,7 tetrazacycloctane and 1,3,5 trinitro-1,3,5triazacylcohexane.
 11. A process for achieving high specific impulse ina solid propellant rocket motor, comprising combusting a solidpropellant containing an oxidizer, polymeric binder and a powdered lightfuel selected from the group consisting of beryllium, boron, aluminum,magnesium, zirconium, titanium, lithium, silicon, aluminum borohydrideand the hydrides of the metals, to form as part of the products ofcombustion a mixture of steam and the oxide of the light metal, allowingsaid mixture to react at combustion temperatures to form the metalhydroxide gas, and cooling said metal hydroxide gas to a temperaturesufficient to release the latent heat of vaporization of said metalhydroxide gas and form metal oxide crystals in a particle size of 0.01to 0.5 microns and steam, said cooling being accomplished by injecting apressurized fuel, selected from the group consisting of alkanes,alkenes, and alkynes, and mixtures thereof, into the metal hydroxide gaswhile it is expanding.
 12. The process of claim 11 wherein saidcombustion temperature is in the range of 3,000* to 4,000* C and saidcooled temperature is in the range of 900* to 1,500* C.
 13. The processof claim 11 wherein the alkanes are selected from the group consistingof methane, ethane, butane, propane, heptane and dodecane, the alkenesare selected from the group consisting of ethylene and propylene and thealkylene is acetylene.
 14. The process of claim 11 wherein said coolingstep is initiated by first passing said products of combustion through acast ring comprising 30-50 percent synthetic rubber compound rich inhydrocarbons, 10-30 percent carbon black and 15-40 percent nitroamine toreact with said products of combustion endothermically to remove heatfrom said products of combustion prior to expansion.
 15. The process ofclaim 14 wherein the synthetic rubber compound is selected from thegroup consisting of polybutadiene, polyurethane,polysulfide-hydrocarbon, polyisobutylene, polyvinylchloride,polyethylene, polypropylene and polyisoprene and the nitroamine isselected from the group consisting of 1,3, 5,7 tetranitro-1,3,5,7tetrazacycloctane and 1,3,5 trinitro-1,3,5 triazacyclohexane.